MathGroup Archive 2003

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Derivative help

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39162] Re: Derivative help
  • From: atelesforos at hotmail.com (Orestis Vantzos)
  • Date: Fri, 31 Jan 2003 19:57:29 -0500 (EST)
  • References: <b1dg35$7ar$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

To begin with, use proper Mathematica syntax to write the body of your
function:
Log[x]^x not ln(x)^x

Even after that, Mathematica is rightfully confused since you don't
specify the variable  of the differentiation (that the expression
should be differentiated as a function of x).
There are two ways to work around this problem:

The first is to define f as you do:
f=Log[x]^x 
and then tell Mathematica to explicitly differentiate it as a function
of x:
D[f,x]

The second way is to define f as a proper Mathematica function:
Clear[f] (* to get rid of the previous definition *)
f[x_]:=Log[x]^x
Now you can write f'[x].
You can even go ahead and write f' but that will return a 'pure
function' (look it up).

Orestis

"Steve Chiang" <stevezx at attbi.com> wrote in message news:<b1dg35$7ar$1 at smc.vnet.net>...
> Hi, all.  I'm new to Mathematica.  I went to the help section for my
> question but it only further confused me.  I'm basically trying to take the
> first derivative of (ln(x))^x.  Here is my syntax: f = (ln(x))^x.  But then
> when I evaluate f ', it says nothing but ((ln(x))^x)' which is nothing new.
> Is this because I didn't specify bounds and that the function may be
> discontinuous over the default bounds in Mathematica?
> 
> Thanks


  • Prev by Date: Re: Derivative help
  • Next by Date: RE: Derivative help
  • Previous by thread: Re: Derivative help
  • Next by thread: RE: Derivative help